This invention relates to a process for the production of an organosilica sol and a surface treating agent containing it.
In building, civil engineering, fiber manufacturing and steel industries, it is general practice to use a surface treating agent for the purpose of imparting members with waterproofness and of improving weatherability thereof.
In recent years, the building and civil engineering industries in particular have been faced with a social problem, i.e. deterioration of concrete caused by penetration of external water into concrete due to low concrete density.
One reason for the unobtainability of dense concrete is as follows. With the introduction of a building construction method including a pumping method, etc., for construction of recent taller concrete buildings, concrete having a higher water content is used in order to improve fluidity.
In order to obtain dense concrete, therefore, a water reducing agent capable of reducing a water content without impairing fluidity is under development, and a good result has been obtained to some extent.
Separately, however, in order to prevent the penetration of external water which causes various troubles, vigorous attempts are under way to develop a surface treating agent capable of penetrating into concrete and imparting the concrete with waterproofness by only applying it onto a concrete surface.
In general, an acrylic rubber waterproofing agent and an epoxy resin water proofing agent are known as a coat type waterproofing agent which is one type of waterproofing agents conventionally used for waterproofing treatment of a concrete outer wall. However, these agents of a coat type have defects that they are required to be applied in a large amount to form a coat, that they cannot take advantage of a texture of a concrete surface, and that they lack water vapor permeability sufficient to prevent dew condensation.
Further, there is another problem that these agents are susceptible to UV rays due to being a coat, and have poor weatherability.
Therefore, it has been and is energetically attempted to develop a waterproofing agent of a penetration type which is considered to be advantageous to improve weatherability in particular.
And, a variety of waterproofing agents of a penetration type such as acryl emulsion-, silicone- and silane-based agents are now commercially available.
However, these agents have advantages and disadvantages. These agents do not have water vapor permeability sufficient to prevent dew condensation, although they can impart members with waterproofness.
It is therefore desired to develop a surface treating agent which has penetrativity into members such as concrete and, at the same time, also has both waterproofness and water vapor permeability.
On the other hand, JP-A-49-126594 discloses a process for imparting organosilica sol with hydrophobic nature by esterification of a silanol group on a silica surface in silica sol with a higher alcohol. And, it is also described that the process can give a stable organosilica sol having a silica concentration of 10 to 30% and containing little impurities. However, this publication discloses nothing concerning the use of the above silica sol as a surface treating agent for members such as concrete, and the like.
The present inventor has made a study to examine whether the organosilica sol disclosed in the above publication can be used as a surface treating agent for members such as concrete, fibers and timber, and found that it is highly acidic as strong as pH of 3.89, the use of it as a surface treating agent deteriorates concrete, corrodes reinforcing steel within concrete, and deteriorates fibers and timber.